763 lines
30 KiB
TeX
763 lines
30 KiB
TeX
\chapter{The Python Profiler}
|
|
\stmodindex{profile}
|
|
\stmodindex{pstats}
|
|
|
|
Copyright \copyright{} 1994, by InfoSeek Corporation, all rights reserved.
|
|
|
|
Written by James Roskind%
|
|
\footnote{
|
|
Updated and converted to \LaTeX\ by Guido van Rossum. The references to
|
|
the old profiler are left in the text, although it no longer exists.
|
|
}
|
|
|
|
Permission to use, copy, modify, and distribute this Python software
|
|
and its associated documentation for any purpose (subject to the
|
|
restriction in the following sentence) without fee is hereby granted,
|
|
provided that the above copyright notice appears in all copies, and
|
|
that both that copyright notice and this permission notice appear in
|
|
supporting documentation, and that the name of InfoSeek not be used in
|
|
advertising or publicity pertaining to distribution of the software
|
|
without specific, written prior permission. This permission is
|
|
explicitly restricted to the copying and modification of the software
|
|
to remain in Python, compiled Python, or other languages (such as C)
|
|
wherein the modified or derived code is exclusively imported into a
|
|
Python module.
|
|
|
|
INFOSEEK CORPORATION DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
|
|
SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
|
|
FITNESS. IN NO EVENT SHALL INFOSEEK CORPORATION BE LIABLE FOR ANY
|
|
SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
|
|
RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF
|
|
CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
|
|
CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
|
|
|
|
|
|
The profiler was written after only programming in Python for 3 weeks.
|
|
As a result, it is probably clumsy code, but I don't know for sure yet
|
|
'cause I'm a beginner :-). I did work hard to make the code run fast,
|
|
so that profiling would be a reasonable thing to do. I tried not to
|
|
repeat code fragments, but I'm sure I did some stuff in really awkward
|
|
ways at times. Please send suggestions for improvements to:
|
|
\code{jar@netscape.com}. I won't promise \emph{any} support. ...but
|
|
I'd appreciate the feedback.
|
|
|
|
|
|
\section{Introduction to the profiler}
|
|
\nodename{Profiler Introduction}
|
|
|
|
A \dfn{profiler} is a program that describes the run time performance
|
|
of a program, providing a variety of statistics. This documentation
|
|
describes the profiler functionality provided in the modules
|
|
\code{profile} and \code{pstats.} This profiler provides
|
|
\dfn{deterministic profiling} of any Python programs. It also
|
|
provides a series of report generation tools to allow users to rapidly
|
|
examine the results of a profile operation.
|
|
|
|
|
|
\section{How Is This Profiler Different From The Old Profiler?}
|
|
\nodename{Profiler Changes}
|
|
|
|
The big changes from old profiling module are that you get more
|
|
information, and you pay less CPU time. It's not a trade-off, it's a
|
|
trade-up.
|
|
|
|
To be specific:
|
|
|
|
\begin{description}
|
|
|
|
\item[Bugs removed:]
|
|
Local stack frame is no longer molested, execution time is now charged
|
|
to correct functions.
|
|
|
|
\item[Accuracy increased:]
|
|
Profiler execution time is no longer charged to user's code,
|
|
calibration for platform is supported, file reads are not done \emph{by}
|
|
profiler \emph{during} profiling (and charged to user's code!).
|
|
|
|
\item[Speed increased:]
|
|
Overhead CPU cost was reduced by more than a factor of two (perhaps a
|
|
factor of five), lightweight profiler module is all that must be
|
|
loaded, and the report generating module (\code{pstats}) is not needed
|
|
during profiling.
|
|
|
|
\item[Recursive functions support:]
|
|
Cumulative times in recursive functions are correctly calculated;
|
|
recursive entries are counted.
|
|
|
|
\item[Large growth in report generating UI:]
|
|
Distinct profiles runs can be added together forming a comprehensive
|
|
report; functions that import statistics take arbitrary lists of
|
|
files; sorting criteria is now based on keywords (instead of 4 integer
|
|
options); reports shows what functions were profiled as well as what
|
|
profile file was referenced; output format has been improved.
|
|
|
|
\end{description}
|
|
|
|
|
|
\section{Instant Users Manual}
|
|
|
|
This section is provided for users that ``don't want to read the
|
|
manual.'' It provides a very brief overview, and allows a user to
|
|
rapidly perform profiling on an existing application.
|
|
|
|
To profile an application with a main entry point of \samp{foo()}, you
|
|
would add the following to your module:
|
|
|
|
\bcode\begin{verbatim}
|
|
import profile
|
|
profile.run("foo()")
|
|
\end{verbatim}\ecode
|
|
%
|
|
The above action would cause \samp{foo()} to be run, and a series of
|
|
informative lines (the profile) to be printed. The above approach is
|
|
most useful when working with the interpreter. If you would like to
|
|
save the results of a profile into a file for later examination, you
|
|
can supply a file name as the second argument to the \code{run()}
|
|
function:
|
|
|
|
\bcode\begin{verbatim}
|
|
import profile
|
|
profile.run("foo()", 'fooprof')
|
|
\end{verbatim}\ecode
|
|
%
|
|
\code{profile.py} can also be invoked as
|
|
a script to profile another script. For example:
|
|
\code{python /usr/local/lib/python1.4/profile.py myscript.py}
|
|
|
|
When you wish to review the profile, you should use the methods in the
|
|
\code{pstats} module. Typically you would load the statistics data as
|
|
follows:
|
|
|
|
\bcode\begin{verbatim}
|
|
import pstats
|
|
p = pstats.Stats('fooprof')
|
|
\end{verbatim}\ecode
|
|
%
|
|
The class \code{Stats} (the above code just created an instance of
|
|
this class) has a variety of methods for manipulating and printing the
|
|
data that was just read into \samp{p}. When you ran
|
|
\code{profile.run()} above, what was printed was the result of three
|
|
method calls:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.strip_dirs().sort_stats(-1).print_stats()
|
|
\end{verbatim}\ecode
|
|
%
|
|
The first method removed the extraneous path from all the module
|
|
names. The second method sorted all the entries according to the
|
|
standard module/line/name string that is printed (this is to comply
|
|
with the semantics of the old profiler). The third method printed out
|
|
all the statistics. You might try the following sort calls:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.sort_stats('name')
|
|
p.print_stats()
|
|
\end{verbatim}\ecode
|
|
%
|
|
The first call will actually sort the list by function name, and the
|
|
second call will print out the statistics. The following are some
|
|
interesting calls to experiment with:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.sort_stats('cumulative').print_stats(10)
|
|
\end{verbatim}\ecode
|
|
%
|
|
This sorts the profile by cumulative time in a function, and then only
|
|
prints the ten most significant lines. If you want to understand what
|
|
algorithms are taking time, the above line is what you would use.
|
|
|
|
If you were looking to see what functions were looping a lot, and
|
|
taking a lot of time, you would do:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.sort_stats('time').print_stats(10)
|
|
\end{verbatim}\ecode
|
|
%
|
|
to sort according to time spent within each function, and then print
|
|
the statistics for the top ten functions.
|
|
|
|
You might also try:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.sort_stats('file').print_stats('__init__')
|
|
\end{verbatim}\ecode
|
|
%
|
|
This will sort all the statistics by file name, and then print out
|
|
statistics for only the class init methods ('cause they are spelled
|
|
with \code{__init__} in them). As one final example, you could try:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.sort_stats('time', 'cum').print_stats(.5, 'init')
|
|
\end{verbatim}\ecode
|
|
%
|
|
This line sorts statistics with a primary key of time, and a secondary
|
|
key of cumulative time, and then prints out some of the statistics.
|
|
To be specific, the list is first culled down to 50\% (re: \samp{.5})
|
|
of its original size, then only lines containing \code{init} are
|
|
maintained, and that sub-sub-list is printed.
|
|
|
|
If you wondered what functions called the above functions, you could
|
|
now (\samp{p} is still sorted according to the last criteria) do:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.print_callers(.5, 'init')
|
|
\end{verbatim}\ecode
|
|
%
|
|
and you would get a list of callers for each of the listed functions.
|
|
|
|
If you want more functionality, you're going to have to read the
|
|
manual, or guess what the following functions do:
|
|
|
|
\bcode\begin{verbatim}
|
|
p.print_callees()
|
|
p.add('fooprof')
|
|
\end{verbatim}\ecode
|
|
%
|
|
\section{What Is Deterministic Profiling?}
|
|
\nodename{Deterministic Profiling}
|
|
|
|
\dfn{Deterministic profiling} is meant to reflect the fact that all
|
|
\dfn{function call}, \dfn{function return}, and \dfn{exception} events
|
|
are monitored, and precise timings are made for the intervals between
|
|
these events (during which time the user's code is executing). In
|
|
contrast, \dfn{statistical profiling} (which is not done by this
|
|
module) randomly samples the effective instruction pointer, and
|
|
deduces where time is being spent. The latter technique traditionally
|
|
involves less overhead (as the code does not need to be instrumented),
|
|
but provides only relative indications of where time is being spent.
|
|
|
|
In Python, since there is an interpreter active during execution, the
|
|
presence of instrumented code is not required to do deterministic
|
|
profiling. Python automatically provides a \dfn{hook} (optional
|
|
callback) for each event. In addition, the interpreted nature of
|
|
Python tends to add so much overhead to execution, that deterministic
|
|
profiling tends to only add small processing overhead in typical
|
|
applications. The result is that deterministic profiling is not that
|
|
expensive, yet provides extensive run time statistics about the
|
|
execution of a Python program.
|
|
|
|
Call count statistics can be used to identify bugs in code (surprising
|
|
counts), and to identify possible inline-expansion points (high call
|
|
counts). Internal time statistics can be used to identify ``hot
|
|
loops'' that should be carefully optimized. Cumulative time
|
|
statistics should be used to identify high level errors in the
|
|
selection of algorithms. Note that the unusual handling of cumulative
|
|
times in this profiler allows statistics for recursive implementations
|
|
of algorithms to be directly compared to iterative implementations.
|
|
|
|
|
|
\section{Reference Manual}
|
|
|
|
\renewcommand{\indexsubitem}{(profiler function)}
|
|
|
|
The primary entry point for the profiler is the global function
|
|
\code{profile.run()}. It is typically used to create any profile
|
|
information. The reports are formatted and printed using methods of
|
|
the class \code{pstats.Stats}. The following is a description of all
|
|
of these standard entry points and functions. For a more in-depth
|
|
view of some of the code, consider reading the later section on
|
|
Profiler Extensions, which includes discussion of how to derive
|
|
``better'' profilers from the classes presented, or reading the source
|
|
code for these modules.
|
|
|
|
\begin{funcdesc}{profile.run}{string\optional{\, filename\optional{\, ...}}}
|
|
|
|
This function takes a single argument that has can be passed to the
|
|
\code{exec} statement, and an optional file name. In all cases this
|
|
routine attempts to \code{exec} its first argument, and gather profiling
|
|
statistics from the execution. If no file name is present, then this
|
|
function automatically prints a simple profiling report, sorted by the
|
|
standard name string (file/line/function-name) that is presented in
|
|
each line. The following is a typical output from such a call:
|
|
|
|
\small{
|
|
\bcode\begin{verbatim}
|
|
main()
|
|
2706 function calls (2004 primitive calls) in 4.504 CPU seconds
|
|
|
|
Ordered by: standard name
|
|
|
|
ncalls tottime percall cumtime percall filename:lineno(function)
|
|
2 0.006 0.003 0.953 0.477 pobject.py:75(save_objects)
|
|
43/3 0.533 0.012 0.749 0.250 pobject.py:99(evaluate)
|
|
...
|
|
\end{verbatim}\ecode
|
|
}
|
|
|
|
The first line indicates that this profile was generated by the call:\\
|
|
\code{profile.run('main()')}, and hence the exec'ed string is
|
|
\code{'main()'}. The second line indicates that 2706 calls were
|
|
monitored. Of those calls, 2004 were \dfn{primitive}. We define
|
|
\dfn{primitive} to mean that the call was not induced via recursion.
|
|
The next line: \code{Ordered by:\ standard name}, indicates that
|
|
the text string in the far right column was used to sort the output.
|
|
The column headings include:
|
|
|
|
\begin{description}
|
|
|
|
\item[ncalls ]
|
|
for the number of calls,
|
|
|
|
\item[tottime ]
|
|
for the total time spent in the given function (and excluding time
|
|
made in calls to sub-functions),
|
|
|
|
\item[percall ]
|
|
is the quotient of \code{tottime} divided by \code{ncalls}
|
|
|
|
\item[cumtime ]
|
|
is the total time spent in this and all subfunctions (i.e., from
|
|
invocation till exit). This figure is accurate \emph{even} for recursive
|
|
functions.
|
|
|
|
\item[percall ]
|
|
is the quotient of \code{cumtime} divided by primitive calls
|
|
|
|
\item[filename:lineno(function) ]
|
|
provides the respective data of each function
|
|
|
|
\end{description}
|
|
|
|
When there are two numbers in the first column (e.g.: \samp{43/3}),
|
|
then the latter is the number of primitive calls, and the former is
|
|
the actual number of calls. Note that when the function does not
|
|
recurse, these two values are the same, and only the single figure is
|
|
printed.
|
|
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{pstats.Stats}{filename\optional{\, ...}}
|
|
This class constructor creates an instance of a ``statistics object''
|
|
from a \var{filename} (or set of filenames). \code{Stats} objects are
|
|
manipulated by methods, in order to print useful reports.
|
|
|
|
The file selected by the above constructor must have been created by
|
|
the corresponding version of \code{profile}. To be specific, there is
|
|
\emph{NO} file compatibility guaranteed with future versions of this
|
|
profiler, and there is no compatibility with files produced by other
|
|
profilers (e.g., the old system profiler).
|
|
|
|
If several files are provided, all the statistics for identical
|
|
functions will be coalesced, so that an overall view of several
|
|
processes can be considered in a single report. If additional files
|
|
need to be combined with data in an existing \code{Stats} object, the
|
|
\code{add()} method can be used.
|
|
\end{funcdesc}
|
|
|
|
|
|
\subsection{The \sectcode{Stats} Class}
|
|
|
|
\renewcommand{\indexsubitem}{(Stats method)}
|
|
|
|
\begin{funcdesc}{strip_dirs}{}
|
|
This method for the \code{Stats} class removes all leading path information
|
|
from file names. It is very useful in reducing the size of the
|
|
printout to fit within (close to) 80 columns. This method modifies
|
|
the object, and the stripped information is lost. After performing a
|
|
strip operation, the object is considered to have its entries in a
|
|
``random'' order, as it was just after object initialization and
|
|
loading. If \code{strip_dirs()} causes two function names to be
|
|
indistinguishable (i.e., they are on the same line of the same
|
|
filename, and have the same function name), then the statistics for
|
|
these two entries are accumulated into a single entry.
|
|
\end{funcdesc}
|
|
|
|
|
|
\begin{funcdesc}{add}{filename\optional{\, ...}}
|
|
This method of the \code{Stats} class accumulates additional profiling
|
|
information into the current profiling object. Its arguments should
|
|
refer to filenames created by the corresponding version of
|
|
\code{profile.run()}. Statistics for identically named (re: file,
|
|
line, name) functions are automatically accumulated into single
|
|
function statistics.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{sort_stats}{key\optional{\, ...}}
|
|
This method modifies the \code{Stats} object by sorting it according to the
|
|
supplied criteria. The argument is typically a string identifying the
|
|
basis of a sort (example: \code{"time"} or \code{"name"}).
|
|
|
|
When more than one key is provided, then additional keys are used as
|
|
secondary criteria when the there is equality in all keys selected
|
|
before them. For example, sort_stats('name', 'file') will sort all
|
|
the entries according to their function name, and resolve all ties
|
|
(identical function names) by sorting by file name.
|
|
|
|
Abbreviations can be used for any key names, as long as the
|
|
abbreviation is unambiguous. The following are the keys currently
|
|
defined:
|
|
|
|
\begin{tableii}{|l|l|}{code}{Valid Arg}{Meaning}
|
|
\lineii{"calls"}{call count}
|
|
\lineii{"cumulative"}{cumulative time}
|
|
\lineii{"file"}{file name}
|
|
\lineii{"module"}{file name}
|
|
\lineii{"pcalls"}{primitive call count}
|
|
\lineii{"line"}{line number}
|
|
\lineii{"name"}{function name}
|
|
\lineii{"nfl"}{name/file/line}
|
|
\lineii{"stdname"}{standard name}
|
|
\lineii{"time"}{internal time}
|
|
\end{tableii}
|
|
|
|
Note that all sorts on statistics are in descending order (placing
|
|
most time consuming items first), where as name, file, and line number
|
|
searches are in ascending order (i.e., alphabetical). The subtle
|
|
distinction between \code{"nfl"} and \code{"stdname"} is that the
|
|
standard name is a sort of the name as printed, which means that the
|
|
embedded line numbers get compared in an odd way. For example, lines
|
|
3, 20, and 40 would (if the file names were the same) appear in the
|
|
string order 20, 3 and 40. In contrast, \code{"nfl"} does a numeric
|
|
compare of the line numbers. In fact, \code{sort_stats("nfl")} is the
|
|
same as \code{sort_stats("name", "file", "line")}.
|
|
|
|
For compatibility with the old profiler, the numeric arguments
|
|
\samp{-1}, \samp{0}, \samp{1}, and \samp{2} are permitted. They are
|
|
interpreted as \code{"stdname"}, \code{"calls"}, \code{"time"}, and
|
|
\code{"cumulative"} respectively. If this old style format (numeric)
|
|
is used, only one sort key (the numeric key) will be used, and
|
|
additional arguments will be silently ignored.
|
|
\end{funcdesc}
|
|
|
|
|
|
\begin{funcdesc}{reverse_order}{}
|
|
This method for the \code{Stats} class reverses the ordering of the basic
|
|
list within the object. This method is provided primarily for
|
|
compatibility with the old profiler. Its utility is questionable
|
|
now that ascending vs descending order is properly selected based on
|
|
the sort key of choice.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{print_stats}{restriction\optional{\, ...}}
|
|
This method for the \code{Stats} class prints out a report as described
|
|
in the \code{profile.run()} definition.
|
|
|
|
The order of the printing is based on the last \code{sort_stats()}
|
|
operation done on the object (subject to caveats in \code{add()} and
|
|
\code{strip_dirs())}.
|
|
|
|
The arguments provided (if any) can be used to limit the list down to
|
|
the significant entries. Initially, the list is taken to be the
|
|
complete set of profiled functions. Each restriction is either an
|
|
integer (to select a count of lines), or a decimal fraction between
|
|
0.0 and 1.0 inclusive (to select a percentage of lines), or a regular
|
|
expression (to pattern match the standard name that is printed). If
|
|
several restrictions are provided, then they are applied sequentially.
|
|
For example:
|
|
|
|
\bcode\begin{verbatim}
|
|
print_stats(.1, "foo:")
|
|
\end{verbatim}\ecode
|
|
%
|
|
would first limit the printing to first 10\% of list, and then only
|
|
print functions that were part of filename \samp{.*foo:}. In
|
|
contrast, the command:
|
|
|
|
\bcode\begin{verbatim}
|
|
print_stats("foo:", .1)
|
|
\end{verbatim}\ecode
|
|
%
|
|
would limit the list to all functions having file names \samp{.*foo:},
|
|
and then proceed to only print the first 10\% of them.
|
|
\end{funcdesc}
|
|
|
|
|
|
\begin{funcdesc}{print_callers}{restrictions\optional{\, ...}}
|
|
This method for the \code{Stats} class prints a list of all functions
|
|
that called each function in the profiled database. The ordering is
|
|
identical to that provided by \code{print_stats()}, and the definition
|
|
of the restricting argument is also identical. For convenience, a
|
|
number is shown in parentheses after each caller to show how many
|
|
times this specific call was made. A second non-parenthesized number
|
|
is the cumulative time spent in the function at the right.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{print_callees}{restrictions\optional{\, ...}}
|
|
This method for the \code{Stats} class prints a list of all function
|
|
that were called by the indicated function. Aside from this reversal
|
|
of direction of calls (re: called vs was called by), the arguments and
|
|
ordering are identical to the \code{print_callers()} method.
|
|
\end{funcdesc}
|
|
|
|
\begin{funcdesc}{ignore}{}
|
|
This method of the \code{Stats} class is used to dispose of the value
|
|
returned by earlier methods. All standard methods in this class
|
|
return the instance that is being processed, so that the commands can
|
|
be strung together. For example:
|
|
|
|
\bcode\begin{verbatim}
|
|
pstats.Stats('foofile').strip_dirs().sort_stats('cum') \
|
|
.print_stats().ignore()
|
|
\end{verbatim}\ecode
|
|
%
|
|
would perform all the indicated functions, but it would not return
|
|
the final reference to the \code{Stats} instance.%
|
|
\footnote{
|
|
This was once necessary, when Python would print any unused expression
|
|
result that was not \code{None}. The method is still defined for
|
|
backward compatibility.
|
|
}
|
|
\end{funcdesc}
|
|
|
|
|
|
\section{Limitations}
|
|
|
|
There are two fundamental limitations on this profiler. The first is
|
|
that it relies on the Python interpreter to dispatch \dfn{call},
|
|
\dfn{return}, and \dfn{exception} events. Compiled C code does not
|
|
get interpreted, and hence is ``invisible'' to the profiler. All time
|
|
spent in C code (including builtin functions) will be charged to the
|
|
Python function that invoked the C code. If the C code calls out
|
|
to some native Python code, then those calls will be profiled
|
|
properly.
|
|
|
|
The second limitation has to do with accuracy of timing information.
|
|
There is a fundamental problem with deterministic profilers involving
|
|
accuracy. The most obvious restriction is that the underlying ``clock''
|
|
is only ticking at a rate (typically) of about .001 seconds. Hence no
|
|
measurements will be more accurate that that underlying clock. If
|
|
enough measurements are taken, then the ``error'' will tend to average
|
|
out. Unfortunately, removing this first error induces a second source
|
|
of error...
|
|
|
|
The second problem is that it ``takes a while'' from when an event is
|
|
dispatched until the profiler's call to get the time actually
|
|
\emph{gets} the state of the clock. Similarly, there is a certain lag
|
|
when exiting the profiler event handler from the time that the clock's
|
|
value was obtained (and then squirreled away), until the user's code
|
|
is once again executing. As a result, functions that are called many
|
|
times, or call many functions, will typically accumulate this error.
|
|
The error that accumulates in this fashion is typically less than the
|
|
accuracy of the clock (i.e., less than one clock tick), but it
|
|
\emph{can} accumulate and become very significant. This profiler
|
|
provides a means of calibrating itself for a given platform so that
|
|
this error can be probabilistically (i.e., on the average) removed.
|
|
After the profiler is calibrated, it will be more accurate (in a least
|
|
square sense), but it will sometimes produce negative numbers (when
|
|
call counts are exceptionally low, and the gods of probability work
|
|
against you :-). ) Do \emph{NOT} be alarmed by negative numbers in
|
|
the profile. They should \emph{only} appear if you have calibrated
|
|
your profiler, and the results are actually better than without
|
|
calibration.
|
|
|
|
|
|
\section{Calibration}
|
|
|
|
The profiler class has a hard coded constant that is added to each
|
|
event handling time to compensate for the overhead of calling the time
|
|
function, and socking away the results. The following procedure can
|
|
be used to obtain this constant for a given platform (see discussion
|
|
in section Limitations above).
|
|
|
|
\bcode\begin{verbatim}
|
|
import profile
|
|
pr = profile.Profile()
|
|
pr.calibrate(100)
|
|
pr.calibrate(100)
|
|
pr.calibrate(100)
|
|
\end{verbatim}\ecode
|
|
%
|
|
The argument to calibrate() is the number of times to try to do the
|
|
sample calls to get the CPU times. If your computer is \emph{very}
|
|
fast, you might have to do:
|
|
|
|
\bcode\begin{verbatim}
|
|
pr.calibrate(1000)
|
|
\end{verbatim}\ecode
|
|
%
|
|
or even:
|
|
|
|
\bcode\begin{verbatim}
|
|
pr.calibrate(10000)
|
|
\end{verbatim}\ecode
|
|
%
|
|
The object of this exercise is to get a fairly consistent result.
|
|
When you have a consistent answer, you are ready to use that number in
|
|
the source code. For a Sun Sparcstation 1000 running Solaris 2.3, the
|
|
magical number is about .00053. If you have a choice, you are better
|
|
off with a smaller constant, and your results will ``less often'' show
|
|
up as negative in profile statistics.
|
|
|
|
The following shows how the trace_dispatch() method in the Profile
|
|
class should be modified to install the calibration constant on a Sun
|
|
Sparcstation 1000:
|
|
|
|
\bcode\begin{verbatim}
|
|
def trace_dispatch(self, frame, event, arg):
|
|
t = self.timer()
|
|
t = t[0] + t[1] - self.t - .00053 # Calibration constant
|
|
|
|
if self.dispatch[event](frame,t):
|
|
t = self.timer()
|
|
self.t = t[0] + t[1]
|
|
else:
|
|
r = self.timer()
|
|
self.t = r[0] + r[1] - t # put back unrecorded delta
|
|
return
|
|
\end{verbatim}\ecode
|
|
%
|
|
Note that if there is no calibration constant, then the line
|
|
containing the callibration constant should simply say:
|
|
|
|
\bcode\begin{verbatim}
|
|
t = t[0] + t[1] - self.t # no calibration constant
|
|
\end{verbatim}\ecode
|
|
%
|
|
You can also achieve the same results using a derived class (and the
|
|
profiler will actually run equally fast!!), but the above method is
|
|
the simplest to use. I could have made the profiler ``self
|
|
calibrating'', but it would have made the initialization of the
|
|
profiler class slower, and would have required some \emph{very} fancy
|
|
coding, or else the use of a variable where the constant \samp{.00053}
|
|
was placed in the code shown. This is a \strong{VERY} critical
|
|
performance section, and there is no reason to use a variable lookup
|
|
at this point, when a constant can be used.
|
|
|
|
|
|
\section{Extensions --- Deriving Better Profilers}
|
|
\nodename{Profiler Extensions}
|
|
|
|
The \code{Profile} class of module \code{profile} was written so that
|
|
derived classes could be developed to extend the profiler. Rather
|
|
than describing all the details of such an effort, I'll just present
|
|
the following two examples of derived classes that can be used to do
|
|
profiling. If the reader is an avid Python programmer, then it should
|
|
be possible to use these as a model and create similar (and perchance
|
|
better) profile classes.
|
|
|
|
If all you want to do is change how the timer is called, or which
|
|
timer function is used, then the basic class has an option for that in
|
|
the constructor for the class. Consider passing the name of a
|
|
function to call into the constructor:
|
|
|
|
\bcode\begin{verbatim}
|
|
pr = profile.Profile(your_time_func)
|
|
\end{verbatim}\ecode
|
|
%
|
|
The resulting profiler will call \code{your_time_func()} instead of
|
|
\code{os.times()}. The function should return either a single number
|
|
or a list of numbers (like what \code{os.times()} returns). If the
|
|
function returns a single time number, or the list of returned numbers
|
|
has length 2, then you will get an especially fast version of the
|
|
dispatch routine.
|
|
|
|
Be warned that you \emph{should} calibrate the profiler class for the
|
|
timer function that you choose. For most machines, a timer that
|
|
returns a lone integer value will provide the best results in terms of
|
|
low overhead during profiling. (os.times is \emph{pretty} bad, 'cause
|
|
it returns a tuple of floating point values, so all arithmetic is
|
|
floating point in the profiler!). If you want to substitute a
|
|
better timer in the cleanest fashion, you should derive a class, and
|
|
simply put in the replacement dispatch method that better handles your
|
|
timer call, along with the appropriate calibration constant :-).
|
|
|
|
|
|
\subsection{OldProfile Class}
|
|
|
|
The following derived profiler simulates the old style profiler,
|
|
providing errant results on recursive functions. The reason for the
|
|
usefulness of this profiler is that it runs faster (i.e., less
|
|
overhead) than the old profiler. It still creates all the caller
|
|
stats, and is quite useful when there is \emph{no} recursion in the
|
|
user's code. It is also a lot more accurate than the old profiler, as
|
|
it does not charge all its overhead time to the user's code.
|
|
|
|
\bcode\begin{verbatim}
|
|
class OldProfile(Profile):
|
|
|
|
def trace_dispatch_exception(self, frame, t):
|
|
rt, rtt, rct, rfn, rframe, rcur = self.cur
|
|
if rcur and not rframe is frame:
|
|
return self.trace_dispatch_return(rframe, t)
|
|
return 0
|
|
|
|
def trace_dispatch_call(self, frame, t):
|
|
fn = `frame.f_code`
|
|
|
|
self.cur = (t, 0, 0, fn, frame, self.cur)
|
|
if self.timings.has_key(fn):
|
|
tt, ct, callers = self.timings[fn]
|
|
self.timings[fn] = tt, ct, callers
|
|
else:
|
|
self.timings[fn] = 0, 0, {}
|
|
return 1
|
|
|
|
def trace_dispatch_return(self, frame, t):
|
|
rt, rtt, rct, rfn, frame, rcur = self.cur
|
|
rtt = rtt + t
|
|
sft = rtt + rct
|
|
|
|
pt, ptt, pct, pfn, pframe, pcur = rcur
|
|
self.cur = pt, ptt+rt, pct+sft, pfn, pframe, pcur
|
|
|
|
tt, ct, callers = self.timings[rfn]
|
|
if callers.has_key(pfn):
|
|
callers[pfn] = callers[pfn] + 1
|
|
else:
|
|
callers[pfn] = 1
|
|
self.timings[rfn] = tt+rtt, ct + sft, callers
|
|
|
|
return 1
|
|
|
|
|
|
def snapshot_stats(self):
|
|
self.stats = {}
|
|
for func in self.timings.keys():
|
|
tt, ct, callers = self.timings[func]
|
|
nor_func = self.func_normalize(func)
|
|
nor_callers = {}
|
|
nc = 0
|
|
for func_caller in callers.keys():
|
|
nor_callers[self.func_normalize(func_caller)]=\
|
|
callers[func_caller]
|
|
nc = nc + callers[func_caller]
|
|
self.stats[nor_func] = nc, nc, tt, ct, nor_callers
|
|
\end{verbatim}\ecode
|
|
%
|
|
\subsection{HotProfile Class}
|
|
|
|
This profiler is the fastest derived profile example. It does not
|
|
calculate caller-callee relationships, and does not calculate
|
|
cumulative time under a function. It only calculates time spent in a
|
|
function, so it runs very quickly (re: very low overhead). In truth,
|
|
the basic profiler is so fast, that is probably not worth the savings
|
|
to give up the data, but this class still provides a nice example.
|
|
|
|
\bcode\begin{verbatim}
|
|
class HotProfile(Profile):
|
|
|
|
def trace_dispatch_exception(self, frame, t):
|
|
rt, rtt, rfn, rframe, rcur = self.cur
|
|
if rcur and not rframe is frame:
|
|
return self.trace_dispatch_return(rframe, t)
|
|
return 0
|
|
|
|
def trace_dispatch_call(self, frame, t):
|
|
self.cur = (t, 0, frame, self.cur)
|
|
return 1
|
|
|
|
def trace_dispatch_return(self, frame, t):
|
|
rt, rtt, frame, rcur = self.cur
|
|
|
|
rfn = `frame.f_code`
|
|
|
|
pt, ptt, pframe, pcur = rcur
|
|
self.cur = pt, ptt+rt, pframe, pcur
|
|
|
|
if self.timings.has_key(rfn):
|
|
nc, tt = self.timings[rfn]
|
|
self.timings[rfn] = nc + 1, rt + rtt + tt
|
|
else:
|
|
self.timings[rfn] = 1, rt + rtt
|
|
|
|
return 1
|
|
|
|
|
|
def snapshot_stats(self):
|
|
self.stats = {}
|
|
for func in self.timings.keys():
|
|
nc, tt = self.timings[func]
|
|
nor_func = self.func_normalize(func)
|
|
self.stats[nor_func] = nc, nc, tt, 0, {}
|
|
\end{verbatim}\ecode
|